1. Field of the Invention
The present invention relates to a novel varnish composition. During manufacturing a glass fiber laminate, a glass fiber cloth is dipped within a novel varnish composition, solvent removal by oven, and then dried to obtain a glass fiber prepreg. The obtained prepreg is laminated onto a copper foil to obtain a novel glass fiber laminate which has high glass transition temperature, good flame retardance, good heat resistance, and low coefficient of thermal expansion, and therefore is suitable for high-performance printed circuit boards.
2. Description of Related Art
A commercially available dual-functional is a brominated epoxy resin which is a mature product and has been used for long time. The long-term modified physical properties of the brominated epoxy resin grant a glass fiber laminate made of the brominated epoxy resin good mechanical properties, electrical properties, physical properties and dimensional stability. Such a modified brominated epoxy resin has great adhesion to glass fiber or copper foil. Therefore, glass fiber laminates made of brominated epoxy resin can be widely used in electronics and aviation industry. However, halogen in high temperature breaks down harmful substances which are harmful to our living environment and human health. Halide-containing substrates have been gradually inhibited for use. European Unit announced to implement related protection regulations such as Directive on the Waste Electronics and Electrical Equipment (referred to as WEEE), and Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (referred to as RoHS) in 2006. Another aspect in the lead-free manufacturing process, a welding process for lead-free packaging and assembly needs a higher temperature (an increase from 220° C. to 260° C.). The glass fiber laminates made of the existing dual-functional brominated epoxy resin cannot meet the requirements. Currently, multi-functional phenolic epoxy or phenolic novolac resin is used to achieve the required glass transition temperature and heat resistance for the lead-free manufacturing process. In a halogen-free substrate, a significant proportion of a polymer of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (referred to as DOPO) and phenol phenolic epoxy resin, or a polymer of DOPO and o-cresol phenolic epoxy resin is used along with dicyandiamide (referred to as Dicy) resin curing agent or multi-functional phenolic resin curing agent such as phenol novolac resin in order to increase the glass transition temperature (referred to as Tg) and heat resistance.
Physical properties of a printed circuit board are mainly determined by three major materials of the glass laminate combination: (1) epoxy (2) filling material and (3) reinforcing material. The development of the substrate continuously requires increasing the glass transition temperature (Tg), the temperature of heat resistance, while decreasing coefficient of thermal expansion (referred to as CTE). For the properties of epoxy resin systems, multi-functional phenolic epoxy resins are commonly used to modify the substrate properties. The multi-functional phenolic epoxy resin is, for example, tetraphenyl ethane phenolic epoxy resin made by Nan Ya Plastics company (trade name NPPN-431). The FR-4 substrate composed by NPPN-431, a phenol curing agent and a glass fiber cloth (grade E glass), the glass transition temperature is 180° C. (according to thermal mechanical analysis) and the heat resistance is above 10 minutes (solder oven at 288° C.). The physical properties of the multi-functional phenolic epoxy resin based laminates are gradually unable to meet the requirements of higher-performance boards.
Therefore, there is a need of a novel varnish composition which overcomes the above disadvantages.